Why are GRU and LSTM better than standard RNNs?
These newer RNNs (LSTMs and GRUs) have greater memory control, allowing previous values to persist or to be reset as necessary for many sequences of steps, avoiding "gradient decay" or eventual degradation of the values passed from step to step. LSTM and GRU networks make this memory control possible with memory blocks and structures called "gates" that pass or reset values as appropriate.